The anatomy scan (Level 2 ultrasound or 20-week scan) is a comprehensive, non-invasive imaging procedure performed during the second trimester. This detailed examination is a standard part of prenatal care, typically scheduled between 18 and 22 weeks of gestation. Its purpose is to assess fetal growth and structural development. The scan uses high-frequency sound waves to create images, allowing the sonographer to check the fetus for structural anomalies or developmental concerns.
Understanding the Typical Timeframe
The anatomy scan is typically longer than routine prenatal ultrasounds due to the detailed checks required. Under ideal circumstances, when the fetus is cooperative and positioned favorably, the scan generally takes between 30 and 45 minutes. Clinics often schedule the appointment for an hour to account for potential delays and ensure the sonographer can systematically cover all anatomical structures. While less common, if the baby is perfectly positioned from the start, some scans may be completed in as little as 20 to 30 minutes.
What Happens During the Examination
Fetal Measurements and Growth
The anatomy scan involves a systematic review of the entire fetus to ensure all major organ systems are developing appropriately. The sonographer begins by taking biometric measurements, including the circumference of the head and abdomen, and the length of the femur. These measurements estimate the baby’s size and weight, helping to confirm gestational age and monitor the growth rate.
Organ System Review
A major focus is the fetal heart, where the technician confirms the presence of four chambers and observes the flow of blood through the valves and major vessels. The brain is also thoroughly examined, checking for the correct size and shape of key structures, including the cerebellum and ventricles. The spine is viewed in both cross-section and long view to ensure the vertebrae are aligned and fully covered by skin.
Additional Checks
The sonographer also assesses the abdominal organs, checking that the stomach, kidneys, and bladder are present and functioning. The face is scanned to look for a cleft lip, and the limbs are checked to ensure the arms, legs, hands, and feet are present and developing normally. Beyond the fetus, the scan includes a check of the umbilical cord, the location of the placenta, and the volume of amniotic fluid.
Factors Influencing Scan Length
The time required to complete the anatomy scan can vary significantly from the standard timeframe due to several factors. The most common delay is the position of the fetus within the uterus. If the baby is curled up, facing the mother’s back, or actively moving, the sonographer may not be able to obtain the necessary images. To encourage the baby to shift position, the technician may ask the patient to stand up, walk around, or drink something cold or sweet.
Maternal body habitus, or a higher body mass index, can also make it challenging for sound waves to penetrate and produce clear images. If a finding is unclear or complex, the sonographer must take extra time to document the observation from multiple angles. If required views cannot be obtained after multiple attempts, the patient may be asked to return for a follow-up scan.
Preparation and Post-Scan Expectations
Preparation
Preparing for the anatomy scan is generally straightforward. Patients are typically advised to wear comfortable, loose-fitting clothing, ideally a two-piece outfit, so the abdomen can be exposed easily. While a full bladder was once common for early ultrasounds, it is often not necessary for the 20-week scan; some facilities prefer an empty bladder for clearer views of the deep pelvic structures.
Results and Follow-Up
After the sonographer has captured all the necessary images and measurements, the procedure is complete. The sonographer focuses on image acquisition and documentation and generally does not provide a verbal interpretation of the findings during the scan. The detailed images and report are sent to a doctor, such as the patient’s obstetrician or a maternal-fetal medicine specialist, for review. The healthcare provider will discuss the results with the patient, either immediately following the scan or at a subsequent appointment.